Cell boards are the building blocks for multi-processor computer systems. Cell boards may include such components as processor(s), memory, application specific integrated circuits (ASICs), and/or input/output (I/O) components. For instance, processor boards, memory boards, and I/O boards may be arranged in a system to form a desired configuration. Further, a single cell board may include a plurality of different types of components. For example, a cell board may include one or more processors, ASIC(s), memory subsystem, and in some cases a power subsystem.
The most common method of interfacing cell boards in a computer system is to provide each cell board with a bus connector and to plug each cell board's bus connector into a matching socket or “slot” mounted to a backplane or motherboard. In general, a backplane provides a communicative interconnection for a plurality of cell boards that are coupled to the backplane. The backplane itself is typically a circuit card that contains sockets to which other cell boards (or “circuit cards”) can be connected. Backplanes may be either active or passive. Active backplanes typically contain, in addition to the sockets, logical circuitry that performs computing functions. In contrast, passive backplanes contain almost no computing circuitry. When multiple cell boards are connected to a single backplane, the resulting arrangement is often referred to as a cabinet (or “card cage”). In higher-end computer systems of this type, cell boards may be removed and replaced in the cabinet without powering down the backplane or any of the slots except the one corresponding to the cell board being replaced. Thus, such cabinets are often implemented for so-called high-availability systems. An example of cell boards and their arrangement in a cabinet is disclosed in U.S. Pat. No. 6,452,789 titled “PACKAGING ARCHITECTURE FOR 32 PROCESSOR SERVER,” the disclosure of which is hereby incorporated herein by reference.
Traditionally, backplanes are implemented as solid structures. For instance, backplanes are typically solid structures that are relatively densely populated with traces and cabling for interconnecting the cell boards coupled thereto. For example, traditional backplanes are generally arranged as a two-dimensional (“2D”) plane (e.g., commonly sized approximately 30 inches by 20 inches) to which cell boards couple, and the 2D plane of the backplane interconnects the cell boards coupled thereto. Traditional backplane designs may have several (e.g., 10) routing layers inside the board, wherein each routing layer comprises traces for interconnecting the cell boards that are coupled to the backplane.
In high-end computing systems, a relatively large number of cell boards may be interconnected within cabinet(s). For example, the Superdome™ server available from Hewlett-Packard Company (“HP”) is available as a 16-way, 32-way, or 64-way server. The 16-way implementation may comprise four cell boards interconnected via a backplane within a cabinet, wherein each cell board may include four central processing units (“CPUs”) for a total of 16 CPUs, and the cell boards may comprise memory (e.g., dual in-line memory modules (“DIMMs”)) implemented thereon for a total of 64 gigabytes (“GB”) of memory available in the 16-way implementation. The 32-way implementation may comprise eight cell boards interconnected via a backplane within a cabinet, wherein each cell board may include four CPUs for a total of 32 CPUs, and the cell boards may comprise memory (e.g., DIMMs) implemented thereon for a total of 128 GB of memory available in the 32-way implementation. The 64-way implementation may comprise sixteen cell boards interconnected via a backplane within a cabinet, wherein each cell board may include four CPUs for a total of 64 CPUs, and the cell boards may comprise memory (e.g., DIMMs) implemented thereon for a total of 256 GB of memory available in the 32-way implementation. Further, as a greater number of cell boards is desired, multiple cabinets that each comprise multiple cell boards may be coupled together to form a high-end server.
Competing design considerations are often encountered when developing such multi-processor computer systems. One design consideration commonly encountered involves cooling the components within the cabinet(s). Because of the heat generated by the components, some type of cooling system is typically included for cooling the components to prevent overheating and resulting improper or failed operation. Because traditional backplanes are solid structures, as described above, cooling systems typically generate air flow in a direction parallel to the backplane (e.g., bottom-to-top air flow). One technique for implementing bottom-to-top air flow is described in U.S. Pat. No. 6,452,789 titled “PACKAGING ARCHITECTURE FOR 32 PROCESSOR SERVER.” Traditional implementations of bottom-to-top air flow (or “front-to-top” air flow, as air may be ingested through the front of the cabinet and re-directed via blowers toward the top of the cabinet) is not optimal for several reasons. First, blowers are typically required for directing the air flow upward, which consume a relatively large amount of space in the cabinets (thus diminishing the space-efficiency of the architecture). Further, as the air moves upward through the cabinet, the air is heated by each cell board that it encounters, thus diminishing the affect of the air in cooling the upper cell board(s). To ensure proper cooling of the upper cell boards, increased air flow is needed, which means that the size of the blowers implemented for generating such increased air flow is undesirably large (and may be undesirably noisy in some architectures).
Another design consideration often encountered in multi-processor computer systems is a desire for an architecture that enables cell boards to be accessed for service (e.g., by a technician). For instance, a cell board may be removable (e.g., hot swappable) from a cabinet for replacing or repairing the cell board. Service access has traditionally been in a direction orthogonal to the system's backplane. For instance, a cell board generally connects orthogonally to a backplane, and such cell board may be connected or removed from the front of a cabinet by moving the cell board in a direction orthogonal to the backplane. Thus, the service access and the air flow are orthogonal to each other in traditional multi-processor computer systems.